A sprain is an injury resulting from the wrenching or twisting of a ligament or muscle of a joint, such as a knee or ankle, characterized by clinical symptoms including swelling, bruising or contusions, pain, and disablement of the joint. A sprain may further be characterized by edema which is an abnormal accumulation of fluid in cells, tissues, or cavities of the body resulting in swelling. Strains are sprains caused by exertion or an acute trauma event. These trauma events can include, for example, an abnormal muscle contraction, a high amount of specifically applied tension, or forced stretching of the muscle of the ligament. These injuries can be extremely debilitating, especially to professional and amateur athletes who can no longer participate in physical activities. In addition, the affected area, most commonly extremities such as the foot, ankle and knee, suffer from reduced range of motion.
Acute inflammation is a response to any type of trauma including trauma events causing a sprain or strain wherein the inflammation protects the tissue and removes any damaged material or tissue from the body. Enzymatic signaling agents including histamine, serotonin, bradykinin, and prostaglandin are normally released as part of the inflammatory process. These agents increase capillary membrane permeability in order to enhance the inflammatory process, but also result in edema from fluid accumulation during the interstitial phase. The signaling agents, therefore, cause the primary symptoms of inflammation: swelling, heat, redness and pain. This initial phase of inflammation can start after one or two days and end after three or four days. In some cases, the damage to the ligament can be even more severe. For example, high ankle sprains involve injury to the ligament above the ankle that joins together the tibia and fibula, or syndesmotic ligament. Regardless of the type of strain or sprain, a single injury has been shown to place the affected extremity at significantly greater risk of re-injury even after the first injury has healed.
Sprains and strains affect a significant number of individuals every year. In the US alone, 14 million patients were admitted into outpatient care for sprains or strains of the foot and ankle alone. Another 20 million patients were admitted for sprains or strains of the knee. Many of these sprains and strains can be extremely debilitating, limiting mobility and causing pain for a long period of time. While these injuries have an impact on the average individual's activity levels, their impact is especially profound for athletes. Athletes, both professional and amateur, are severally limited by these injuries and often reinjure themselves because they return to the physical activity too soon ignoring the long time period necessary for complete healing of the injury. In the US alone, the costs charged to Medicare for outpatient strains or sprains were $390M in 2011, while the costs charged to private insurance were $1.2B in 2011.